The instant application should be granted the priority date of Apr. 24, 2004, the filing date of the corresponding German patent application 10 2004 020 063.7.
The present invention relates to a method for break separation of pieces that can be re-assembled or their starting materials.
In connection with the separation of re-assemblable pieces or their starting materials, break separation has emerged as the preferred method for effecting such separation in those areas involving a high degree of junction precision, in conjunction with an economical manufacture, such as, for example, in the combustion engine area, the separation of the connecting rod bearing cover from bearings or the crankshaft bearing cover from the bearing cover housings.
The break separation is effected via differing working steps involving the pieces, with these working steps always following the same technical method course. Initially, a groove is configured into the piece to be subjected to break separation, whereby the groove partially or completely follows the desired path of the break line along the contour of the piece. The configuring of the groove into the piece can be effected in various ways; the literature provides extensive information in this connection. The thus-produced groove has the purpose of initiating the separation along the separation path upon the application of the forces that effect the break separation of the piece. The actual break separation then follows in a manner in which a force is applied perpendicular to the desired break surface, this force breaking the piece at the desired location. In practice, however, it has come about that the actual break path very frequently deviates from the desired break path. The causes therefor are multi-fold. One cause can be traced to the material itself, brittle molded materials being better suited for break separation than ductile materials, examples of which are forged piston rods. In addition to the material itself, latent stresses, impurities, or non-homogeneity of the basic piece can be causes of an unsatisfactory break process.
It is known, for example from DE 100 22 884, that, to favorably influence the breakage, the break region can be made brittle through a thermal treatment locally limited relative to the remainder portions of the piece in the course of a structure transformation, this treatment leading to a local, multi-axial stress condition. This embrittlement can be effected in various ways. In connection with expanded laser grooves such as are described, for example, in DE 196 17 402 A1, the desired break line is melted along the material, and the melt remainder is blown away or vaporized so that there results a through groove or a line of serially arrayed blind holes. The edge regions of the groove or the holes are embrittled via the formation of corresponding structures because the heat is conducted away very rapidly from the very small deposition or melted area into the remainder portions of the piece. The multidimensional stress conditions connected with the embrittlement can lead to microscopic hard tears which are in fact, desired, but which nonetheless, like the stress conditions, run into selected angles along the desired break line and cause, like the stress conditions, a “wandering away” of the break line, if the break is initiated via application of the break separation force.
It is further known from EP 0 661 125 A1 that, to favorably influence the break, a force is initially applied in the direction of the break separation force that will later be applied to the piece, whereby this pre-stress force lies below the elastic limit of the pieces to be separated. In this manner, the force that is necessary for the actual separation can be minimized, which sets the stage for achieving the steepest possible slope (rate of rise) of the actual break force to be applied. The steep slope influences the initiation of the break and the break path in a positive manner but, however, in ensuring that the static pre-stress is effective in relatively large regions of the piece, it cannot preclude the wandering away of the break line from the desired path that results from the above-described causes.